1. Field of the Invention
The present invention relates to demulsification, and more particularly to resolution of emulsions formed during the preparation of pharmaceuticals and other bioprocessing applications.
2. Description of the Prior Art
In a standard method for preparation of pharmaceuticals such as antibiotics, for example, penicillin or substances obtained from microorganisms such as bacteria, algae or fungi (streptomycin, erythromycin, efrotomycin, etc.), a culture of microorganisms or enzymes or both in a nutriment medium, such as vegetable oil in a water base, ferments to produce a desired pharmaceutical. However, the fermented mass has been found to comprise not only the desired pharmaceutical, but also other organic fermentation products such as a biomass of microorganisms or enzymes, uncoverted nutriment medium, water and surfactant. Thus, the desired pharmaceutical must be extracted from the undesirable components of the fermented mass.
The desired pharmaceutical is extracted first by adjusting the pH of the fermented mass, if required. Depending on the particular culture and desired pharmaceutical, the pH is adjusted either up or down, as necessary, by addition of a base or an acid, respectively, to precipitate or partition the desired pharmaceutical. Shortly before or after adjustment of the pH, an extracting solvent, typically an organic phase such as amyl acetate, methyl ethyl ketone, methyl isobutyl ketone, amyl alcohol, butyl alcohol, benzyl alcohol or the like, is added to extract the desired pharmaceutical from the water phase to the organic phase, and the phases are separated.
Often the water and oil phases are commingled in the form of an emulsion, and so good separation can be difficult to achieve. Similar emulsions may also be encountered in other bioprocessing applications. It is believed that the organic phase typically is emulsified or dispersed in the water phase, although it is possible that the water phase is dispersed or emulsified through the organic phase or that actually an emulsion is dispersed or emulsified through another phase such as water.
Nevertheless, depending on the components, some emulsions eventually break by themselves, that is, such emulsions have only "temporary stability" and over time and with the aid of gravity or centrifugation the emulsion separates into distinct layers. However, more commonly, a demulsifier is added to encourage or initiate separation by gravity or centrifugation. Ordinarily, sodium chloride or another inorganic salt or a demulsifier such as DEMULSO I or III (trade designations of Petrolite Corp.) is employed as a demulsifier.
In any event, upon separation, a solvent phase and a water phase are formed. The solvent phase comprises the desired pharmaceutical, solvent and small amounts of water and other impurities, such as organic material, the structure of which may be similar to that of the desired pharmaceutical and other undesirable components dissolved in the solvent. The water phase comprises the remaining components, including the biomass of the microorganisms or enzymes, and there may be a small amount of the desired pharmaceutical dissolved in the water and contained in the biomass.
The solvent phase may be cleaned further after separation from the water phase by adding clean water. By adjusting the pH of the mixture, the desired pharmaceutical sometimes can be shifted to either the water or the organic phase in order to simplify isolation of the pharmaceutical. By a second separation step, the desired phase may be isolated. If the addition of water forms a secondary emulsion, separation may be accomplished as described for the first emulsion.
When the phase containing the desired pharmaceutical has been cleaned to the desired level, excess solvent or water, depending on the phase in which the pharmaceutical is held, can be evaporated off.
Conventional methods for demulsification and separation of phases have several drawbacks. For example, although inorganic salts such as sodium chloride are routinely used as demulsifiers, they do not perform as well as desired. Thus, the phase separation can take place more slowly than desired, and the separation tends to involve a relatively large, indistinct interface, with poor segregation of components into the separate phases. For example, a significant portion of the desired pharmaceutical is often entrapped within cells of the biomass. As a result, recovery of the pharmaceutical typically has been found to be as low as 80%.
Other demulsifiers have been used to resolve such emulsions, but are limited in that they resolve only certain of such emulsions. Moreover, although they resolve the phases more quickly, clearly and thoroughly than do the inorganic salts, even better and faster phase separation is desirable.
On the other hand, a variety of demulsifiers have been used in conjunction with emulsions formed in extraction and production of petroleum-based oils from oil fields. Conventionally, oil field chemistry has not been considered in relation to pharmaceutical processes. In particular, oil field demulsifiers conventionally have not been considered as demulsifiers of emulsions formed during the preparation of pharmaceuticals.
Several factors may contribute to the fact that oil field demulsifiers conventionally have not been considered for resolving emulsions produced in the preparation of pharmaceuticals. Oil field techniques and pharmaceutical processes are extremely disparate arts and one skilled in one of the arts typically would be unknowledgable about the other art. Moreover, even if one were skilled in both arts, oil field emulsions generally are recognized to respond differently to demulsifiers than do emulsions formed in pharmaceutical preparation. Thus, oil field demulsifiers generally have not been employed in resolving pharmaceutical related emulsions.